In related art, a technology is known in which maximum rated current of a power supply is variably set based on a temperature in a method of controlling the output from the power supply. In addition, a technology is known in which, when the electric power used in the main body of a device exceeds threshold power in a state in which a power supply unit is used as a power supply source of the main body of the device, the power supply source of the main body of the device is switched to the power supply unit and a secondary battery. Furthermore, a technology is known in which, when a device uses power exceeding a power supply capacity of a converter, the electric power of the device is covered by the electric power from the converter and the electric power from a secondary battery. Furthermore, a technology is known in which when supply of direct-current power from a main power supply is stopped, the direct-current power is supplied from a power supply different from the main power supply to a load.
The electric power supplied from a power supply unit is varied with the operating status of a load connected to an output path of the power supply unit. However, with the technologies in the related art, if a peak of the variation (hereinafter also referred to as “peak power”) exceeds an estimated value, the voltage of the output path of the power supply unit may be decreased.
The followings are reference documents.                [Document 1] Japanese Laid-open Patent Publication No. 2001-075659,        [Document 2] Japanese Laid-open Patent Publication No. 2011-223786,        [Document 3] Japanese Laid-open Patent Publication No. 2007-274748, and        [Document 4] Japanese Laid-open Patent Publication No. 9-322433.        